The present invention relates generally to a replaceable cartridge for a printing machine and more particularly to a technique for controlling a degree to which developer material is developed on a photoreceptive member of the printing machine.
In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced for selectively discharging the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development and transfer, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways.
A process referred to as "highlight color imaging" has been accomplished by employing basic xerographic techniques. The concept of tri-level, highlight color xerography is described in the following patent:
U.S. Pat. No. 4,078,929
Patentee: Gundlach
Issued: Mar. 14, 1978
U.S. Pat. No. 4,078,929 discloses the use of tri-level xerography as a means to achieve single-pass highlight color imaging. As disclosed therein the charge pattern is developed with toner particles of first and second colors. The toner particles of one of the colors are positively charged and the toner particles of the other color are negatively charged. In one embodiment, the toner particles are supplied by a developer which comprises a mixture of triboelectrically relatively positive and relatively negative carrier beads. The carrier beads support, respectively, the relatively negative and relatively positive toner particles. Such a developer is generally supplied to the charge pattern by cascading it across the imaging surface supporting the charge pattern. In another embodiment, the toner particles are presented to the charge pattern by a pair of magnetic brushes. Each brush supplies a toner of one color and one charge. In yet another embodiment, the development systems are biased to about the background voltage. Such biasing results in a developed image of improved color sharpness.
In highlight color xerography as taught by Gundlach, the xerographic contrast on the charge retentive surface or photoreceptor is divided into three levels, rather than two levels as is the case in conventional xerography. The photoreceptor is charged, typically to -900 volts, and exposed imagewise, such that one image corresponding to charged image areas (which are subsequently developed by charged-area development, i.e. CAD) stays at the full photoreceptor potential (V.sub.cad or V.sub.ddp). V.sub.ddp is the voltage on the photoreceptor due to the loss of voltage while the photoreceptor remains charged in the absence of light, otherwise known as dark decay. Another image is exposed to discharge the photoreceptor to its residual potential, i.e. V.sub.dad or V.sub.c (typically -100 volts), which V.sub.c corresponds to discharged area images that are subsequently developed by discharged-area development (DAD). The background area is exposed so as to reduce the photoreceptor potential to halfway between the V.sub.cad and V.sub.dad potentials, (typically -500 volts) and is referred to as V.sub.white. The CAD developer is typically biased about 100 volts closer to V.sub.cad than V.sub.white (about -600 volts), and the DAD developer system is biased about 100 volts closer to V.sub.dad than V.sub.white (about -400 volts). As will be appreciated, the highlight color need not be a different color but may have other distinguishing characteristics. For example, one toner may be magnetic and the other non-magnetic.
It is generally well known to control and adjust particular parameters of an electrophotographic printing machine. For example, individual control signals can be used to adjust operating elements of a printing machine, such as controlling development by control of the ratio of toner particles to carrier granules in the developer material and the electrical bias applied to the developer roller. Other control techniques compare a signal measuring the reflected light from a clean photoconductive member to a signal reflected from a developed test patch formed thereon. The resultant error signal regulates toner dispensing to control the concentration of toner particles in the developer material on the photoconductive surface. Generally, the density of the developer material developed on the test patch is monitored by an infrared densitometer. In various applications, the photoreceptive member includes at least two document zones and an interdocument zone disposed therebetween. Preferably, an image from a document is developed in the document zone while the test patch is developed in the interdocument zone. Typically, the test patch is formed in the interdocument zone so as not to interfere with imaging in the document zone. The following patents and applications pertain to arrangements for generating and monitoring toner density of developed test patches disposed in interdocument zones:
U.S. patent application Ser. No. 07/755,193
Applicants: Scheuer et al.
Filed: Sep. 5, 1991
U.S. patent application Ser. No. 07/755,197
Applicants: Berman et al.
Filed: Sep. 5, 1991
U.S. Pat. No. 4,999,673
Patentee: Bares
Issued: Mar. 12, 1991
U.S. Pat. No. 5,019,859
Patentee: Nash
Issued: May 28, 1991
The following patent is directed toward a cleaning arrangement for a highlight color printing system:
U.S. Pat. No. 5,175,590
Patentees: Frankel et al.
Issued: Dec. 29, 1993
U.S. Pat. No. 5,175,590 discloses an arrangement including a plurality of corona devices disposed about a photoreceptor. In one example, optimal transfer and detack of non-black and black developer materials from respective document zones appears to be obtained when the applied currents of the corona devices are set at preselected levels.
Recently, electrophotographic reproducing machines, such as the one described above, have been developed which use one or more replaceable subassembly units, familiarly termed cartridges. One typical cartridge comprises a toner supply and the necessary supporting hardware therefor assembled in a single unit designed for insertion and removal into and out of the machine. When the cartridge is used up, the old cartridge is removed and a new one substituted. Other replaceable cartridges including developer cartridges, photoreceptor cartridges, etc., may also be envisioned for this purpose.
The following patent, the pertinent portions of which are incorporated herein by reference, is directed toward an example of a cartridge, also referred to as a "customer replaceable unit" ("CRU").
U.S. Pat. No. 4,961,088
Patentees: Gilliland et al.
Issued: Feb. 1, 1994
U.S. Pat. No. 4,961,088 discloses a system for monitoring replaceable cartridges in printers or copiers. Each replaceable cartridge includes an EEPROM (Electrically Eraseable Programmable Read Only Memory). The EEPROM associated with each cartridge may be programmed with an identification number and means for retaining a count of prints or copies made with the unit. The EEPROM may also be designed to retain a cartridge replacement warning count and a termination count at which the cartridge is disabled from further use.
Other CRUs employing EEPROMs are disclosed in the following patents:
U.S. Pat. No. 5,272,503
Patentees: LeSueur et al.
Issued Dec. 21, 1993
U.S. Pat. No. 5,283,613
Patentee: Midgley, Sr.
Issued: Feb. 1, 1994
U.S. Pat. No. 5,272,503 discloses a system in which a printing machine operating parameter is adjusted, with a controller, in accordance with a value stored in CRU memory and updated in response to a predetermined period of subassembly usage.
It has been found that employing CRUs in a highlight color printing machine that uses many different color toners can be problematic. More particularly, as will appear from the description below, various setpoints are preferably set in a color printing machine to accommodate for a given toner type. These values corresponding to the various setpoints are stored in nonvolatile memory ("NVM"). When many colors are interchanged with the color printing machine, by way of different CRUs, a relatively large number of values, corresponding to the setpoints required for the different CRUs, must be stored in NVM. While this approach is acceptable for a printing machine with virtually unlimited NVM, it is unsuitable for those situations where memory usage must be economized.
The following reference anticipates such economization of memory for a paper cassette: